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        var val = 33;
        console.log(typeof val) // "number"
        val = '葵花宝典'
        console.log(typeof val) // "string"
        val = { name: '东方不败' }
        val = function () {
            console.log('人生自古谁无种，留取丹心断命根')
        }
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        console.log(val.xx) // undefined
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